The present invention relates to syringe assemblies for administering fluid medications to patients and more specifically to syringe assemblies commonly referred to as two compartment syringes wherein the powder medicament and diluent are isolated in separate compartments of the syringe for storage purposes and including means for mixing a powder medicament and diluent just prior to use.
Two compartment syringes are not new per se. These syringe assemblies generally comprise an outer barrel, vial or container for the powder medicament, and inner barrel, vial, or container telescopically mounted in the outer barrel for the diluent and a plunger moveable axially in the inner barrel for mixing and discharging the medicament through a needle mounted at the discharge end of the outer barrel. Generally, these assemblies include some form of sealing means mounted at the discharge end of the inner barrel which normally isolates the diluent and powder medicament until ready for use. In some instances the sealing means is in the form of a diaphragm which is supported over the discharge end of the inner barrel and which upon increase of hydraulic or fluid pressure in the inner barrel caused by actuation of the plunger either releases or is burst to permit flow of diluent to the powder medicament chamber for preparation of the medicament. Even though these assemblies are generally satisfactory, it has been found that they do have certain disadvantages and drawbacks. For example, the bursting diaphragm type presents the problem of particulate matter mixing with the medicament which can cause difficulty in discharging the syringe contents and there is also the danger of injecting particulate matter into the patient.
Additionally, it has been found that in some instances these sealing arrangements do not provide an adequate moisture-vapor barrier and consequently the assemblies do not possess the necessary desired long shelf life. It is noted that migration of vapor to the powder medicament may effect its efficacy.
An example of a two compartment syringe incorporating bursting and so-called slide aside diaphragms is shown and described in the Brignola application, Ser. No. 06/034,461 now U.S. Pat. No. 4,331,146 entitled SYRINGE ASSEMBLY, owned by the assignee of the present application. In the two compartment syringes illustrated, the sealing means is in the form of a thin Teflon diaphragm which is supported over the discharge end of the inner barrel by a rubber plunger which has a through opening. In one form of the diaphragm, the return flange is of uniform configuration so that actuation of the plunger axially in the inner barrel causing increase in fluid or hydraulic pressure bursts the diaphragm and diluent can flow freely to the powder compartment. Bursting, of course, may present the problem and danger of particulate matter and it is therefore somewhat undesirable. In another form, the return flange of the diaphragm is of a predetermined configuration so that the seating force is non-uniform about the periphery and hence when the internal hydraulic pressure increases, the diaphragm does not burst but displaces laterally to permit flow of diluent to the powder compartment. In some instances, the entire diaphragm may be displaced and this presents the problem of clogging or jamming the discharge opening in the outer barrel and prevent easy discharge of the mixed medicament. Further, the barrels are usually made of polymerized glass and consequently the desired inert Teflon diaphragm is difficult to seat accurately over the discharge end of the inner barrel with the inner plunger engaging over it since it tends to slip and not adhere sufficiently to the glass. Thus assembly is tedious and time consuming.
In accordance with another two compartment syringe shown in German Pat. No. 1,491,785 the inner barrel has a pintle which projects through an opening in a diaphragm snugly seated over the discharge end of the inner barrel and the inner barrel is provided with a series of small discharge ports circumferentially spaced outboard of the centrally disposed pintle. Now fluid pressure acting through these small openings displaces the axial end face of the diaphragm outwardly to permit flow to the powder compartment. Even though this arrangement avoids the problem of particulate matter, it is virtually impossible to provide the necessary tight seal to prevent migration of moisture and thus this syringe has a very short unacceptable shelf life.
The two compartment syringe shown in the Cheney Pat. No. 3,685,514 issued Aug. 22, 1972, shows a similar arrangement. However, in this assembly the inner barrel has a small centrally located discharge port and the diaphragm which snugly embraces the outer discharge end of the inner barrel has a series of circumferentially spaced openings normally confronting the axial end face of the inner barrel radially outwardly of the centrally located discharge port. Thus, when the plunger is actuated to increase hydraulic pressure in the inner barrel, the thin face of the diaphragm is deflected outwardly to permit flow from the central discharge port in the inner barrel to the radially outwardly located discharge openings in the front face of the diaphragm. Here again, there is no problem of particulate matter. However, the seal is not sufficient to ensure a good long shelf life. Furthermore, in both assemblies inadvertent pressure on the actuating plunger during shipment or even while in storage, can result in small quantities of diluent entering the powder chamber and destroying the efficacy of the product. Furthermore, this inadvertent actuation would not be readily ascertainable by the user.
Cohen, U.S. Pat. No. 3,838,689 issued Oct. 1, 1974 for DISPOSABLE SYRINGE WITH SLIT VALVE shows an arrangement wherein the valve or diaphragm separating the two compartments has a slit which normally seals the two compartments and which opens on increase in hydraulic pressure to permit flow of diluent for mixing purposes. Here again, migration of vapor to the powder compartment over a period of time is inevitable and consequently, these syringes have a relatively short, unacceptable shelf life. The slit is usually formed in the plunger-type diaphragm when the elastic material, usually rubber, is in a generally relaxed state and it has been found that the slit tends to reknit or bond itself shut when the plunger is placed under compression in the syringe and consequently the rather thick wall of the plunger is extremely difficult or impossible to burst when it is desired to actuate the syringe. This is particularly true with syringes that have been stored for normal relatively long periods prior to use.
Shaw, U.S. Pat. No. 3,477,432 issued Sept. 21, 1964, shows several embodiments of two compartment syringes. In accordance with one embodiment, the diaphragm at the discharge end of the inner barrel has a hinged plug which frictionally seats in the discharge end to normally seal the two compartments. This is good from the standpoint of eliminating particulate matter but has the shortcoming described above, an inadequate seal.
Ratcliff, et al U.S. Pat. No. 2,869,534 issued Aug. 23, 1957, for INJECTOR shows an arrangement wherein the inner barrel terminates in a nozzle and a cap fits over the nozzle to normally seal the chamber. The cap is discharged completely from the nozzle of the inner barrel upon increased hydraulic pressure in the inner barrel when arming or preparing the syringe for mixing the diluent and powder. The cap floating in the outer chamber may jam the discharge opening and hinder easy discharge of the medicament.
With the above in mind, it is an object of the present invention to provide a new and improved syringe assembly which is characterized by novel features of construction and arrangement providing an effective moisture-vapor barrier between the diluent and powder compartments thereby ensuring a long shelf life and which may be actuated to mix the components without creation of any material particulate matter thereby ensuring the integrity and safety of the product dispensed. To this end, the assembly includes a plug made of a resilient material, such as rubber, which normally seats in the discharge end of the inner barrel having a pintle or teat-like projection on its outer axial end face and a plunger assembly mounted on the discharge end of the inner barrel which snugly engages in the outer barrel and has a chamber formed therein of an axial length greater than the axial length of the plug and of a diameter slightly greater than the diameter of the plug and formed with a series of openings in the front face of the chamber. By this arrangement, when the inner barrel actuating plunger is moved forwardly, the plug is displaced into the plunger chamber and is confined therein in a position to permit flow of the diluent from the inner barrel around the plug to the outer barrel. The teat-like projection engages generally centrally relative to the openings in the front face of the plunger to ensure good flow of diluent around the plug during the mixing cycle. It has been found that this arrangement provides an effective seal and eliminates the problem of particulate matter. Furthermore, the parts of the assembly are relatively easy and economical to make and can be assembled quickly and easily to provide a well-sealed arrangement ensuring long shelf life and also one that eliminates the problems of particulate matter or difficulty in preparing for mixing characteristic of some of the prior syringes discussed above.